The invention refers to a disposable syringe that has been improved in determinate structural aspects with the object of achieving better performance and greater functional effectiveness than conventional syringes.
The object of the invention is to obtain a disposable syringe of the type comprising a main body in which the chamber for the liquid to be injected is determined, and a needle with a coupling cone on the end of said main body. The needle is complemented by a kind of sheath that protects and sterilises it. The syringe includes peculiarities with respect to the system for coupling the cone to the main body and coupling the protective sheath of the injection needle which, obviously, complements the assembly.
There is a type of disposable syringe made up of a cylindrical, hollow body, which is open at its rear end to allow the movement of a rod corresponding to a piston that moves inside said cylindrical body for pushing and/or absorbing the liquid. The cylindrical body determines a chamber between its front end and the piston that can move axially in the same. Said axial rod ends in a kind of flattening or expansion to allow it to be manually actuated by the user.
This type of syringe is complemented by the corresponding needle which is housed in a covering in the form of a hood or sheath that constitutes a means for protecting the needle and also achieving hermetic sealing and the corresponding sterilisation, since the needle has a cone on its rear end for coupling to the corresponding end or neck established for this purpose on the front end of the main body of the syringe. The rear end of the sheath meets the perimeter of said coupling cone, thus achieving a hermetic seal and maintaining sterilisation of the needle, so that when the unit is going to be used, it is sufficient to couple the needle holder which slightly protrudes with respect to the rear end of the sheath over the neck of the body of the syringe, and then to extract or separate the sheath for the syringe to be ready to use.
As is clear, the coupling between the cone of the needle and the neck of the body of the syringe must be watertight to keep the liquid insulated inside the main body of the syringe, or what amounts to the same thing, in its corresponding chamber.
However, sometimes during handling, in the coupling and subsequent extraction of the protective sheath of the needle, a slight uncoupling and/or mobility of said cone occurs with respect to the neck of the body of the syringe, thus losing its hermetic seal and making it possible for air to enter the chamber, or even an unwanted exit of liquid.
When the protective sheath of the needle is being separated, it may also become badly aligned due to the tilting that may occur on the coupling cone, all of which means the risk of losing water-tightness of the liquid to be injected, or even problems of another kind with respect to the effectiveness and proper insertion of the needle in the muscular mass of the patient, as well as an irregular injection of liquid.
The syringe of the type referred to in the foregoing section, has a series of peculiarities on the basis of which the problems and drawbacks mentioned above are resolved.
More specifically, the first novel characteristic of the syringe of the invention is that the neck provided in the front end of the main body of the syringe, upon which the cone of the needle must be coupled, projects lengthwise with respect to the end in which the front end or part of the body extends, to define a large ring-shaped channel between said extension and the neck of the coupling. In said ring-shaped channel the rear end of the cone is housed, as well as the rear end of the sheath, although it is limited in its penetration in order to be able to separate it afterwards.
Another novel characteristic, is that the front extension of the main body of the syringe has an inner helicoidal fluting which determines a kind of thread for holding a ring-shaped rim provided in the rear part of the coupling cone. The latter thus remains completely held in place once it has been inserted into the concentric neck of the main body of the syringe, which makes it possible to extract and separate the sheath once the cone of the needle is coupled by pressure since, logically, to prevent the loss of water-tightness and therefore maintain sterilisation of the needle until it is to be used, the latter must be coupled to the body of the syringe with the sheath fitted and then finally extracted. Said sheath also includes a perimetric rear rim, which stops against the inner, slightly trunco-conical surface of the extension provided with the helicoidal fluting mentioned above, as the cone fits onto a complementary conical surface corresponding to the concentric neck of the main body. The liquid to be injected exits, pushed by the piston, through said neck and is injected by means of the needle that is coupled in the way described above.
In this way, an effective hermetic or watertight seal is achieved in the coupling of the cone to the body of the syringe, which will remain permanently intact since said cone is held in place by the inner fluting of the axial extension of the syringe""s body, thus allowing the sheath to be extracted by pulling outwards without the coupling cone undergoing any movement or tilting during this operation of separation of the sheath.